Adding to reputation

why cant you let me thank(by adding to their reputation) the same person if he/she has helped me in two different cases. (I cant add to a persons reputations just because I have given one could, and is for some other is that its the same person who runs to help me..)

If you see, I have two threads where I had been helped by the same person who took pains to answer every query (however basic they were). But I cant add to the reputation for the second time do you think you are encouraging a helping person when you dis-allow this to show on their stats?